Cast alloys



Sept. 18. 1956 Rupture Life, Hrs.

w. w. DYRKACZ ETAL 2,763,547

CAST ALLOYS 2 Sheets-Sheet l W 25,000 psi (20 Cr 2ONi) 30,000 psi (20 Cr 20 Ni) Boron Fig. l

' INVENTOR. Wasil W, Dyrkucz Edward E. Reynolds and William E Blutz 5 ATTORNEY United States Patent 2,763,547 CAST ALLOYS Wasil W. Dyrkacz, N ewtonville, Edward E. Reynolds,

Loudonville, and William E. Blatz, Troy, N. Y., as-

signors to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania Application June 9, 1955, Serial No. 514,344

5 Claims. (Cl. 75-171) This invention relates to cast alloys, and in particular to cast austenitic alloys having high rupture strength at elevated temperatures.

This application is a continuation-in-part of our copending application Serial No. 423,142 filed April 14, 1954, now abandoned.

Alloys containing in excess of 9% cobalt, from about 12% to about 22% chromium, about to about 30% nickel, about 2% to about 6% each of molybdenum, tungsten and columbium, about 0.1% to 0.70% carbon and the balance substantially iron, have been known as evidenced by Patent No. 2,397,034 issued March 19, 1946, to G. Mohling. An alloy of such composition is widely used in the wrought form by the industry and is known to the trade as 8-816 alloy. Such alloy has good physical characteristics in the wrought condition at temperatures in the neighborhood of 1500 F., but is too weak for satisfactory application for use at temperatures in excess of 1500 F. and in particular at temperatures of 1600 F. to 1700 F.

An object of this invention is to produce a cast austenitic alloy having high rupture strength at elevated temperatures of 1500 F. to 1700 F.

Another object of this invention is to produce a cast alloy having a rupture life in excess of 200 hours at an elevated temperature of 1600 F. and a stress of 25,000 p. s. i., together with good rupture ductility.

A further object of this invention is to produce a cast article of manufacture from an austenitic allowof 0.10% to 0.70% carbon, 30.0% to 70.0% cobalt, 18.0% .to 30.0% chromium, up to 22.0% nickel, 2.0% to 6.0% molybdenum, 2.0% to 6.0% tungsten, 2.0% to 6.0% of metals selected from the group consisting of columbium and tantalum, 0.60% to 1.30% boron and not more than 7.0% iron with incidental impurities, and which will have a long rupture life at elevated temperatures of l500 F. to 1700 F.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which:

Figure l is a graph, the curves of which illustrate the effect of the boron content on the rupture life of alloys of this invention at an elevated temperature of 1600" F. under different load conditions;

Fig. 2 is a graph, the curves of which illustrate the effect of chromium on the rupture life of alloys of this invention having two different nickel contents; 1 and Fig. 3 is a graph, the curve of which illustrates the effect of the nickel content on the rupture life of the alloy of this invention at an elevated temperature of 1600" F. under a load of 30,000 p. s. i.

In practicing this invention boron is employed in critical amounts with the other alloying elements in balanced relationship to thereby enable the production of a cast alloy which, in the cast form, will have a rupture strength at 1600 F. which is equal to or better than the rupture strength of the alloy of the Mohling Patent No. 2,397,034 in the wrought condition at a temperature of only 1500 F. In producing the cast alloy of this invention it has been found that the amount of boron is critical and that the chromium and nickel contents must be closely controlled in order to obtain maximum rupture life at elevated temperatures of 1500 F. to 1700 F. under conditions of stress.

The cast austenitic alloy of this invention will be better understood by reference to the following table in which is listed the broad range of composition, a preferred range of composition and an optimum composition.

TABLE I Broad Preferred Optimum, Element Range, Range, Percent Percent Percent by Wt. by Wt. by Wt.

0. 10-0. 0. 32-0. 52 0. 4 2.0 max. 0.5-1. 5 1. 0 1.0 max. 1. 20-0. 60 0. 4 30. 0-70. 0 i 40. 0-60. 0 53.0 1850-30. 0 22. 5-27. 5 25. 0 0. 22. 0 0. l2. 5 5. 0 2. 06.\0 3.5-5. 5 4. 0 2. 06..0 3. 5-5. 5 4. 0 2. 0-6. 0 3. 55-5 4. 0 0. 60-1. 30 0. 8-l. 20 1. 0 7.0 max. 5 0 max. Bal

The :alloys of Table I may also contain incidental impurities gSLlCh as sulfur and phosphorus in amounts up .to 0. 05 maximum, but such impurities are preferably maintained at not more than 0.03%.

In producing the alloys of this invention it was also found that the carbon, chromium and nickel contents were somewhat critical with respect to their effect on the rupture life of the cast alloy at elevated temperatures. It has also been found to be essential to maintain the boron content within a definite range to obtain the outstanding results to be disclosed hereinafter. Thus, while the inclusion of boron in amounts up to about 3.25% has a beneficial effect and improves the rupture life of the cast alloy at elevated temperatures with respect to similar alloys free from boron but inthe wrought form and precipitation hardened, in

order that the cast alloy of this invention will have a rupture life at 1600 F. as long as or better than the rupture life of an identical boron-free wrought and precipitation hardened alloy at a temperature of 1500 F., the boron content must be maintained in the range of 016% to 1.30% and preferably in the range of 0.8% to 1.20%.

Asillustrative of the critical nature of the boron content of the cast alloy of this invention, reference may be had to the following table in which a number of alloys and their compositions are listed and which were made in perfecting this invention and in demonstrating the efiect of boron:

TABLE II Alloy Mn Si Cr Ni Fe W Mo Ob Ta B Number TABLE III of this invention having a boron content of from 0.6% to 1.30% have a rupture life at 1600 F. under a stress of 25,000 p. s. i. in excess of 200 hours, the maximum rupture life being obtained where the boron content is in the neighborhood of about 1.0%.

The same etfect of the boron is found at elevated temperatures of 1600 F. when the stress is increased to 30,000 p. s. i. and the boron content ranges from 0.6% to 1.30% with the nominal composition given hereinbefore. Likewise, when the nominal composition is changed to a 25% chromium, 5% nickel composition,

Efiect of Boron on Rupture Properties of Cast Alloy 1500 F.35,000 p. s. i. 1600 F.25,000 p. 3.1. 1700 F.-18,000 p. s. 1.

Heat B Rupture Elong. Red. of Rupture Elong. Red. of Rupture Elong. Red. of

Time (Per- Area Time (Per- Area Time (Per- Area (Hr.) cent) (Per- (Hr.) cent) (Per- (Hr.) cent) (Percent) cent) cent) The critical nature of the boron content between 0.6% and 1.30% is evident from the rupture life recorded under the test conditions in Table III. The effect of the boron on the rupture life of the alloys listed in Table III as tested at 1600 F. under a stress of 25,000 p. s. i. is graphically illustrated by curve 10 of Fig. 1 of the drawings. As is evident from the results given in Table III and the graphic illustration of curve 10, the alloys the same unusual peaking effect in the rupture life as tested at 1600 F. under a stress of 30,000 p. s. i. is found, as the boron content varies from 0.6% to 1.30% and in particularjfrom 0.8% to 1.2%. Such alloys are listed in the following table, it being noted that alloys F-666 through F669 are of the 25% chromium, 5% nickel nominal composition, whereas alloy $11 568, F-386 and F-S96 are of the 20% chromium, 20% nickel nominal c p s t o 7 When the cast alloys of Table IV were tested at 1500 F., 1600 F. and 1700 F. under dilferent load conditions, the following results were obtained:

TABLE VII and 18 are clearly illustrative of the outstanding results Eflect of chromium and nickel on rupture properties of cast alloys containing 0.9 boron 1500 F.45,000 p. s. l. 1600 F.-30,000 p. s. i. 1700 F.-20,000 p. s. l.

Alloy Cr Red. Red. Red. No. Rupture Elong. of Rupture Elong. of Rupture Elong. or

Time (Per- Area Time (Per- Area Time (Per- Area (Hr.) cent) (Per- (Hr.) cent) (Pen (Hr.) cent) (Percent) I cent) cent) Ni Alloys F-570- 15. 54 12 11. 2 9. 2 31 12.0 21. 8 20 17. 1 51 F-569 19. 96 28 13. 3 34. 7 41 11. 3 30. 0 29 27 58 F-63 25. 28 130 10. 7 13. 4 257 11. 6 31. 8 253 17. 5 33. 2 F-618- 30. 88 32 9 12. 2 30 14 24. 6 33 12. 2 55 7 F635 35. 52 38 7. 5 10. 7 18 15. 3 31. 6 8 38. 4 54 5 5% Ni Alloys F-586- 13.64 17 9. 9 11. 5 13 26. 8 16 23 34. 3 F619 20.08 19 17 17. 2 116 17 21 93 17 27 F-667- 25. 84 329 9. 3 15. 2 283 11 18.8 220 11. 4 21. 1 F-63 30. 24 45 9. 9 12. 7 70 13 27. 8 35 8. 2 35 1 -588- 34. 42 24 15 33 27 18 52. 2 15 28 41. 7

% Ni Alloys F-587- 10. 84 4 6. 5 7 8 8 12.2 5 16.5 34 F-585- 13.58 6 7. 4 20 17' 12 31. 6 18 23. 5 35 F-63 20. 12 83 9. 2 17 4 120 8. 4 11.6 89 19 37 111-670. 25.32 201 11.6 11 5 314 14. 5 29. 1 156 10. 5 28. 3 F-620- 30. 64 37 12. 1 16 59 16 36. 4 32 12. 4 50. 6 F636 34. 73 4 2 2 16 8.2 11.4 s 21.8 34. 2

15% Ni Alloys F584 13. 58 11 7 10 18 17 21. 8 16 14. 5 22. F632 20. 32 109 9 8 11. 4 166 8 5 19. 6 101 11 22. 8 F541 25. 00 106 12 16 174 12 2 24. 0 131 16. 5 35. 2 F616 30. 36 13 9 2 18 30 12 29. 1 50 22 36 9 F-637. 35. 84 5 9 8. 5 10 13. 5 20. 8 9 24 2 N1 Alloys F583 13. 60 6 9. 1 14 3 .14 13 5 20. 1 9 11. 8 20. 7 F-596- 20. 48 76 8. 7 20 3 128 16 22. 2 89 14. 5 30. 4 F-629- 25. 50 80 16 33 5 177 13. 5 26. 7 249 17. 5 26 F-617- 29. 63 11. 6 34 20. 5 23. 5 15 29 36. 2

% Ni Alloys F589 13. 85 7 7. 5 10 19 11.9 23 5 9 18 31. 3 F-641- 19. 71 27 8. 9 15. 2 113 13. 5 19 3 83 17. 5 29. 6 F640 25. 68 73 11. 1 16. 7 96 18 15 8 107 14. 5 25 8 F639 29. 99 9 8. 1 13. 7 21 13 18 28 20.5 31

% Ni Alloy As is evident from the test data given for the alloys of- 7 Table VI and reported in Table VII, the rupture life when tested at 1600 F. and 30,000 p. s. i. was a maximum in all cases at about 25 chromium as the nickel varied from 0% to 22%, it being noted that as the nickel also increased therefrom to 25 and 30%, such higher nickel. contents had a detrimental effect on the rupture life. From the" different tests conducted it became apparent that a maximum of about 22% nickel is the most that can be tolerated in the alloy of this invention and still obtain a good rupture life.

Referring to Fig. 2 of the drawing, the effect of the chromium content for two different levels of nickel content on the rupture life of the cast alloys made and tested is graphically illustrated. In Fig. 2, curve 16 represents the eifect of the chromium content as it varies from about 13% to 35% on the rupture life of the cast alloy containing about 5% nickel as tested at 1600 F. and 30,000 p. s. i., such curve being based on the test results given in Table VII for the series of the nominal 5% nickel alloys. Curve 18 is a similar curve in that it graphically illustrates the effect of the'chromium content on the rupture life of the cast alloy containing about 20% nickel as tested at 1600 F. and 30,000 p. s. i., such curve obtained in rupture life Where the chromium ranges from 18% to 30% and demonstrate that the optimum content of the-chromium should be at about 25 When the test results given in Table VII for the alloys of the optimum 25% chromium content are correlated with the different nickel contents of from 0% up to 30%, the etfect of the nickel on the rupture life of the cast alloys as tested at 1600 F. under a load of 30,000 p. s. i.

can be and is graphically illustrated as by curve 20 of Fig.

3 of the drawing. As clearly shown by curve 20, good results are obtained even in the absence of nickel, whereas optimum results are obtained with nickel in the range of from 5% to 12.5% and with the nickel preferably at about 10% tents exert a maximum effect in extending the rupture life 10f the cast alloys of this invention. In substantially all casesit has been found that a maximum rupture life is obtained with the alloys of this invention where the carbon content is maintained at about 0.4%. This has been found to be true under different conditions of test such 9 as at 1500 F. under a load of 45,000 p. s. i., at 1600 F. under a load of 30,000 p. s. i. and at 1700 F. under a load of 20,000 p. s. i.

The cast alloys of this invention have outstanding rupture strength which makes possible their use as cast articles of many diiterent shapes and sizes Where a long rupture life at elevated temperatures is required. Thus the alloy of this invention can be successfully cast by precision casting methods or otherwise into the shape of turbine blades and other articles of manufacture for use in jet engines and gas turbines, and because of the high rupture strength will permit an increase in the operating temperature of such apparatus to a blade temperature in excess of 1600 F.

The alloys of this invention can be produced by standard steel mill practice and can be readily reproduced by anyone skilled in the art. In practice the alloy can be poured into small ingots or pigs which are sold directly to the producer of cast articles, or the pigs can be further melted and cast into forms such as fingers or shot which can be used by the consumer in the making of precision castings.

We claim:

1. A cast austenitic alloy consisting of 0.10% to 0.70% carbon, up to 2.0% manganese, up to 1.0% silicon, 30.0% to 70.0% cobalt, 18.0% to 30.0% chromium, up to 22.0% nickel, 2.0% to 6.0% molybdenum, 2.0% to 6.0% tungsten, 2.0 to 6.0% of metal from the group consisting of columbium and tantalum, 0.60% to 1.30% boron, and not more than 7.0% iron with incidental impurities.

2. As an article of manufacture, a casting formed from an austenitic alloy consisting of 0.10% to 0.70% carbon, up to 2.0% manganese, up to 1.0% silicon, 30.0% to 70.0% cobalt, 18.0% to 30.0% chromium, up to 22.0% nickel, 2.0% to 6.0% molybdenum, 2.0% to 6.0% tungsten, 2.0 to 6.0% of metal from the group consisting of columbium and tantalum, 0.60% to 1.30% boron, and

not more than 7.0% iron with incidental impurities, said casting being characterized by its high rupture strength at elevated temperatures of 1500" F. to 1700 F.

3. A cast austenitic alloy consisting of 0.32% to 0.52% carbon, 0.5% to 1.5% manganese, 0.20% to 0.60% silicon, 22.5% to 27.5% chromium, up to 12.5% nickel, 40.0% to 60.0% cobalt, 3.5% to 5.5% molybdenum, 3.5% to 5.5% tungsten, 3.5% to 5.5% of metal selected from the group consisting of columbium and tantalum, 0.8% to 1.2% boron, and not more than 5.0% iron with incidental impurities.

4. A cast austenitic alloy consisting of about 0.4% carbon, about 1.0% manganese, about 0.4% silicon, about 25.0% chromium, about 5.0% nickel, about 53.0% cobalt, about 4.0% molybdenum, about 4.0% tungsten, about 4.0% of metal selected from the group consisting of columbium and tantalum, about 1.0% boron and the balance iron with incidental impurities.

5. As an article of manufacture, a casting formed from an austenitic alloy consisting of 0.32% to 0.52% carbon, 0.5% to 1.5% manganese, 0.20% to 0.60 silicon, 22.5% to 27.5% chromium, up to 12.5% nickel, 40.0% to 60.0% cobalt, 3.5% to 5.5% molybdenum, 3.5% to 5.5% tungsten, 3.5% to 5.5% of metal selected from the group consisting of columbium and tantalum, 0.8% to 1.2% boron, and not more than 5.0% iron with incidental impurities, the cast article being characterized by having a rupture life of not less than about 200 hours at a temperature of 1600 F. under a stress of 25,000 p. s. i.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,490 Mohling Apr. 10, 1945 2,397,034 Mohling Mar. 19, 1946 2,469,718 Edlund May 10, 1949 2,515,775 Epremian July 18, 1950 

1. A CAST AUSTENITIC ALLOY CONSISTING OF 0.10% TO 0.70% CARBON, UP TO 2.0% MANGANESE, UP TO 1.0% SILICON, 30.0% TO 70.0% COBALT, 18.0% TO 30.0% CHRONIUM, UP TO 22.0% NICKLEL, 2.0% TO 6.0% MOLYBDENUM, 2.0% TO 6.0% TUNGSTEN, 2.0 TO 6.0% OF METAL FROM THE GROUP CONSISTING OF COLUMBIUM AND TANTALUM, 0.60% TO 1.30% BORON, AND NOT MORE THAN 7.0% IRON WITH INCIDENTAL IMPURITIES. 